Erratic spark
 

Got a good one for y'all. 87' 944S. Sometimes it starts, sometimes it don't. Some times it runs perfect, sometimes it hovers around 300rpms then dies. Backfires, (belts are new and perfect). DME tested, coil tested, ECU been video micro scoped for solder joints, ICU is only a few years old due to fender bender but can't find a shop with the correct connector to test it?, one question still lingers, I traced the reference and speed sensors and seems that the speed (lower one) isn't plugged into anything. Does it go to the plug below the O2 plug? Well it's dirty like nothing was ever attached to it ( rubber 3 prong socket). Tach does bounce even in no start situation. So, after putting a spark light on it ( when it won't run) it lights up erratically, bright-dim, not uniformly with rotation at all. I know the S model is a little bit tricky in the ignition systems, maybe that's why the only made um two for 2 years. Still, when it runs, it runs strong, when it don't , well it don't. Turns over all day long, just smellin' the garage up with fuel. Outside temp don't seem to matter. It's been anywhere from 52 to 88 here in St Louis. I'm at a loss and can't afford just buying parts to eliminat suspects. Been through that o'l bad new cheap part thing.

"I traced the reference and speed sensors and seems that the speed (lower one) isn't plugged into anything. Does it go to the plug below the O2 plug? Well it's dirty like nothing was ever attached to it ( rubber 3 prong socket)."

Not sure I follow. The car wouldn't even start without that sensor connected , as I understand it. And no tach bounce. Also, it should be easy to see where it plugs in: there should be two electrical connectors side by side, more or less directly above the sensors themselves.

I think you should post a picture or two so knowledgeable people can work out which sensor we're actually talking about here.

Update on the bad spark issue. It was the ignition control module. Was under the impression that if they go there gone, but they obviously can become weak and run perfect....then nothing. Thanks for all the imput

Not sure how much we all helped, but glad to hear it's running well now.

Reminds me: I've been meaning to clean out my ICV for the last year...

erratic spark
 

The 944S has only one sensor on the bell housing. The other sensor "hall sender" is on the distributer housing.

How did you discover the ignition control module as the culprit?